(a) Field of the Invention
The present invention relates to a wireless network discovery method for intersystem handover, and a multi-mode terminal and a service server using the wireless network discovery method.
(b) Description of the Related Art
It is expected that, in a next generation wireless network, internet protocol (IP)-based wireless packet access networks having various characteristics for satisfying subscriber's increasing requirements including a high quality multimedia service, a single contact number, and a low price, will concurrently exist and have overlapped service coverage areas. In a heterogeneous wireless network environment, service coverage areas of wireless networks respectively having different characteristics and inter-working with each other are overlapped so that a service subscriber may selectively connect to an optimum network according to location, propagation environment, service characteristics, and user preferences.
To provide optimized performance and a seamless service to a service subscriber in the heterogeneous wireless networks, it is highly required to perform an inter-system handover (ISHO) between the heterogeneous wireless networks, the inter-system handover for changing an access path of a current service to the optimum wireless network according to a location of a multi-mode terminal (hereinafter, also referred to as a “terminal”) and the propagation environments. To perform the ISHO between the heterogeneous wireless networks, it is firstly required that the terminal acknowledges a propagation environment of a system other than a serving system that receives a current service so as to discover wireless networks for providing services at a current location of the terminal.
In addition, to provide a wideband data rate for the multi-mode terminal having high speed mobility that is one of service goals of the next generation wireless network, it is required to quickly and efficiently discover the wireless networks for providing the services. It is highly required to provide a method for efficiently discovering the wireless network so that the next generation wireless network is successfully realized.
In addition, while it is preferred that a multi-modem of the multi-mode terminal may be realized by a single modem integrating modem modules respectively having different characteristics, the multi-modem will be realized by providing a plurality of separate modems to a terminal before a method for integrating multi-modems is fully developed.
Accordingly, when a wireless network discovery operation is performed, in the multi-mode terminal having the plurality of separated modems, there is a problem in that power consumption may be increased according to a multi-modem activation mechanism or that the wireless networks may not be quickly discovered.
Conventional network discovery methods include a periodic modem activation (PMA) method and an ideal coverage based periodic modem activation (IcPMA) method.
Firstly, in the PMA method, modem interfaces of the multi-mode terminal are activated to measure strengths of signals received from the wireless networks. In this case, a modem activating period differently affects a quick network discovery and an efficient power use, which are main performance parameters for discovering the wireless network. That is, while the wireless network may be quickly discovered when the modem activating period is set to be short, the power consumption of the terminal may be increased since the modem is frequently activated. In addition, while a power source may be efficiently used when the modem activating period is set to be long, an optimum service environment may not be quickly provided to a user since it is slow to discover the wireless network to be used.
In the IcPMA method, location based techniques including a radio frequency (RF) triangulation technique and a global positioning system (GPS) technique are used to quickly discover the wireless network. The IcPMA method is to actively control the modem activating period of the terminal based on information on ideal service coverage of the plurality of wireless networks and a current location of the terminal, the current location provided from a location-based service (LCS) server.
In the IcPMA method, the unnecessary power consumption may be prevented since the ideal service coverage including actual service coverage which varies in relation to time and space is set and the modem activating period for discovering a received signal is set to be short when the terminal enters the ideal service coverage.
However, the power consumption of the terminal may be steeply increased by only using the location-based technique provided to the multi-mode terminal, and therefore it is not efficient. In addition, a service coverage area of a hot-spot wireless network in a metropolitan area does not have a fixed form such as a conceptual propagation model. Therefore, even when the modem is activated in the ideal coverage area, a propagation signal of the wireless network having the hot-spot may not be detected. Therefore, the ideal service coverage area is set to be similar to a geographical shape of the actual service area, but to set the ideal service coverage as above, it is required to continuously detect a location of a hot-spot wireless access base station. Therefore, there is a problem in managing the wireless network (i.e., in managing information on the location of an access base station).
In Korean Patent Laid-Open Publication No. 2004-58934 (published in Jul. 5, 2004) as the prior art, a method for processing a multi-mode service of a mobile communication terminal using a global positioning system (GPS) has been disclosed, in which the GPS measures information on a location of a dual-mode terminal and a method for performing handover between a 2 G system and a 3 G system by using the information is provided.
In the above Korean Patent Laid-Open Publication No. 2004-58934, the multi-mode terminal uses the GPS technique in the dual-mode terminal to discover and select heterogeneous networks rather than activating heterogeneous modems.
In addition, Korean Patent Laid-Open Publication No. 2005-52172 (published on Jun. 2, 2005) provides a method in which the multi-mode terminal determines a network system by using information on a location of a terminal detected by the GPS.
In the above Korean Patent Laid-Open Publication No. 2005-52172, when network system information is not obtained in a multi-mode communication environment (code division multiple access (CDMA), wideband code division multiple access (WCDMA), global system for mobile communication (GSM)), a communication mode at a corresponding location is determined by using the information on the current location obtained by the GPS, and information on a corresponding network system is obtained based on the determined communication mode to perform the communication.
In addition, a transaction entitled “An Adaptive Scheme for Vertical Handoff in Wireless Overlay Networks” by Wen-Tsuen et al. in the IEEE ICPADS 04 (published in 2004) discloses a method for detecting heterogeneous systems by using the GPS without activating all the modems in the multi-mode terminal.
In the above transaction in IEEE ICPADS 04, when locations of a terminal and a base station of a predetermined system are obtained by using the GPS and the terminal is in an imaginary propagation radius of the base station of the predetermined system, a handover to the corresponding system may be performed.
However, since additional techniques including the GPS technique are required in the above prior art, there are problems in that costs are increased and battery consumption is increased at the terminal.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.